Anger can damage the person's mental and physical health. As the poster Bill3 pointed out in his response; anger is a coping mechanism. If your family is overwhelming your boyfriend's time, imposing on him (which is what it sounds like from what you wrote), I think I'd snap at them too.

So, that makes me think, that both you and your boyfriend need to team together and impose much stricter boundaries with your overbearing family members, whose intentions may or may not be genuine, because their imposition could eventually destroy the trust between you and your boyfriend as resentment builds. He will resent you for not being stronger around them when your family members impose on your time and his time, and you will feel like a victim of "who do I please more: my boyfriend or my family?" This is just based on what you've written.

Do you think you may have codependency issues at all? Codependent people tend to have weaker boundaries, because they are the caretakers, the scapegoats, the perfectionists. If you've done everything that your family has told you to do; what school to attend, what major to choose, then I think you need to also address that issue with yourself. Why do you allow them to continue to tell you (and now your boyfriend) what to do, and how to live your lives?

Since your boyfriend's anger is passive and overwhelmed, I think he could benefit from seeing an anger specialist, because he can learn to replace his angry responses with other emotional responses to situations as they arise.

And yes, anger does get worse if what's causing it, (the root cause, usually from the family of origin), isn't addressed and repaired. Staying the same for him (and for you) is unhealthy both mentally and physically.